This invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to improving the reliability of a disc drive by reducing the areal density of the disc drive.
Data storage devices of the type known as xe2x80x9cWinchesterxe2x80x9d disc drives, or hard disc drives, are typically utilized as primary data storage devices in modern computer systems. Such disc drives record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless direct current (dc) spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 revolutions per minute.
Data are stored on and retrieved from the tracks using an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically comprise an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator bearing housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator bearing housing opposite to the coil, the actuator bearing housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted.
Thus, when current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator bearing housing rotates, the heads are moved radially across the data tracks along an arcuate path.
The movement of the heads across the disc surfaces in a disc drive utilizing a voice coil actuator system is typically under the control of a closed loop servo system. In a closed loop servo system, specific data patterns used to define the location of the heads relative to the disc surface are prerecorded on the discs during the disc drive manufacturing process. These servo data patterns can be recorded exclusively on one surface of one disc and continuously read, or can be recorded at the beginning of each user data recording location and read intermittently between intervals of recording or recovering of user data. Such servo systems are referred to as xe2x80x9cdedicatedxe2x80x9d and xe2x80x9cembeddedxe2x80x9d servo systems, respectively.
It is also common practice in the industry to divide each of the tracks on the disc surface into a number of sectors (also referred to as xe2x80x9cdata blocksxe2x80x9d and xe2x80x9cdata fieldsxe2x80x9d) for the storage of user data. The ratio of space used by sectors on a track to the space unoccupied by data is commonly used in designing and manufacturing disc drives. The measure of the amount of data per arcuate distance along a track is expressed in terms of kilobits per inch, or kBPI. Similarly, the density of data per unit area on the surface of a disc is referred to as the areal density and expressed in units of gigabits per square inch.
It is widely accepted in the relevant industry that a disc drive with fewer BPI will perform more reliably than a drive of comparable capacity with more BPI. Specifically, a disc drive with fewer BPI can take advantage of a lower data transfer rate. A lower transfer rate in turn provides significantly improved read performance.
Generally, in a single disc drive, all sectors are formatted such that they contain a specific number of bytes. The industry standard for sector size is 512 bytes. The actual physical space a sector occupies may vary radially across the disc. In order to improve drive read/write performance, manufacturers often elongate the sectors residing on tracks disposed near the center of the disc drive. Additionally, only an integer number of sectors may be written on any one track. Incomplete sectors are not utilized in the storage of user data.
Sector spacing is a function of format overhead and controller capabilities. Format overhead includes, but is not limited to, servo control limits, phase locked oscillator fields, and the placement of servo burst information. Consequently, tracks adjacent to one another which contain the same number of complete sectors have different quantities of unused space between sectors.
The identity of each sector, and thus the radial and circumferential location of the disc relative to the heads, is determined by prerecorded sector ID information included in the servo data pattern. In typical servo systems, a header is recorded at the beginning of each user data sector, which includes, among other information, the track number and sector number, thus providing to the servo system a continually updated status on the location of the actuator relative to the disc.
In addition to the restriction of placing only an integer number of sectors on each track, the linear velocity at which each track rotates must also be taken into consideration. The linear velocity of each track is a function of the angular velocity of the disc and the specific radial distance from the center of the disc to the track. Because the tracks at the outer edges of the disc drive are rotating at a higher linear velocity than the inner tracks, it is necessary to compensate for the radial velocity gradient by manipulating the characteristic parameters of the read/write heads.
In some disc drives of the current generation, the sectors are not only used to store user data, but also can be used to provide the tuning information which adapts the read/write channel to the particular combination of recording medium and head for each disc surface. It is common in such disc drives for the sector on the disc surface to include control fields used to automatically adjust the gain of the write and read amplifiers used to control the recording and recovery of user data. Thus, prior to any attempt to access user data, the read/write channel is optimized for that sector.
To efficiently manage the parametric diversity of sectors radially dispersed throughout the disc, many in the industry divide the surface of the disc drive into contiguous, concentric read/write zones containing an irregular number of tracks per zone. Such zonal allocation permits a manufacturer to assign specific read/write parameters for each distinct zone. Additionally, a manufacturer may designate a common number of sectors per track for each distinct zone. Through an iterative process, manufacturers typically adjust the transfer rate and the location of the inner track of each zone to reach a desired capacity within the preselected data density profile. Because the inner track of each zone has a higher BPI than all other tracks in that zone, adjusting the location of the inner zone determines the maximum BPI profile for all other tracks in that zone. For additional discussion of zone based recording techniques, see U.S. Pat. No. 4,799,112 issue to Bremmer et al. and U.S. Pat. No. 5,087,992 issued to Dahandeh et al., both of these references being assigned to the assignee of the present invention.
Often, the properties of each zone are summarized in a zone table that provides density of data information, track information, and data transfer rate information. The goal of designing a zone table involves meeting a required capacity point while maintaining a given BPI profile.
The above mentioned convention of fixing the transfer rate in a dependent fashion to the BPI profile unnecessarily reduces the degrees of freedom available during disc formatting. Accordingly, there is a significant need for a method of disc zoning that provides maximum storage capacity at favorable data transfer rates.
The present invention is directed to improving disc drive performance by reducing areal data storage density while maintaining data storage capacity.
As exemplified by preferred embodiments, a disc drive is provided with a head adjacent a rotatable disc having a recording surface.
Operational performance of the disc drive is improved by selecting a total user data storage capacity for the recording surface. Next, a total number of user data fields is selected to meet the data storage capacity, each data field storing a selected number of bits.
The data fields are distributed among a plurality of concentric zones, each zone having a plurality of data tracks each having a common number of data fields so that each track in each zone has a selected data storage capacity. The data fields of each zone are written at a first write frequency. The zones are defined in relation to a data density profile defining a desired relationship between a data density at an innermost track of an innermost zone of the recording surface and a data density at an innermost track of an outermost zone of the recording surface.
A second write frequency is thereafter selected for each zone equal to or less than the first write frequency that will achieve the selected data storage capacity of each track in said zone, thereby reducing data density of at least selected tracks. The second write frequency is thereafter used during normal disc drive operations.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.